反射基类

/*
 * Copyright (C) 2012 Square, Inc.
 * Copyright (C) 2013 Google, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package dagger.internal;

import java.lang.reflect.AccessibleObject;


/**
 * Provides a point of configuration of the basic resolving functions within Dagger, namely
 * that of Module handling, injection binding creation, and static injection.  A plugin must
 * provide all resolution methods
 */
public abstract class Loader {
  private final Memoizer<ClassLoader, Memoizer<String, Class<?>>> caches =
      new Memoizer<ClassLoader, Memoizer<String, Class<?>>>() {
        @Override protected Memoizer<String, Class<?>> create(final ClassLoader classLoader) {
          return new Memoizer<String, Class<?>>() {
            @Override protected Class<?> create(String className) {
              try {
                return classLoader.loadClass(className);
              } catch (ClassNotFoundException e) {
                return Void.class; // Cache the failure (negative case).
              }
            }
          };
        }
      };

  /**
   * Returns a binding that uses {@code @Inject} annotations, or null if no valid binding can
   * be found or created.
   */
  public abstract Binding<?> getAtInjectBinding(
      String key, String className, ClassLoader classLoader, boolean mustHaveInjections);

  /**
   * Returns a module adapter for {@code moduleClass} or throws a {@code TypeNotPresentException} if
   * none can be found.
   */
  public abstract <T> ModuleAdapter<T> getModuleAdapter(Class<T> moduleClass);

  /**
   * Returns the static injection for {@code injectedClass}.
   */
  public abstract StaticInjection getStaticInjection(Class<?> injectedClass);

  /**
   * Loads a class from a {@code ClassLoader}-specific cache if it's already there, or
   * loads it from the given {@code ClassLoader} and caching it for future requests.  Failures
   * to load are also cached using the Void.class type.  A null {@code ClassLoader} is assumed
   * to be the system classloader.
   */
  protected Class<?> loadClass(ClassLoader classLoader, String name) {
    // A null classloader is the system classloader.
    classLoader = (classLoader != null) ? classLoader : ClassLoader.getSystemClassLoader();
    return caches.get(classLoader).get(name);
  }

  /**
   * Instantiates a class using its default constructor and the given {@link ClassLoader}. This
   * method does not attempt to {@linkplain AccessibleObject#setAccessible set accessibility}.
   */
  protected <T> T instantiate(String name, ClassLoader classLoader) {
    try {
      Class<?> generatedClass = loadClass(classLoader, name);
      if (generatedClass == Void.class) {
        return null;
      }
      @SuppressWarnings("unchecked")
      T instance = (T) generatedClass.newInstance();
      return instance;
    } catch (InstantiationException e) {
      throw new RuntimeException("Failed to initialize " + name, e);
    } catch (IllegalAccessException e) {
      throw new RuntimeException("Failed to initialize " + name, e);
    }
  }

}